Table 3.

How the hypotheses account for experimental observations

Hypothesis	Observation
	1	2	4	5	6	7	8	9, 10
0. Protein only	—	—	—	—	—	N	N	Y
1. MPF oscillates	Y	Y	Y	Y	M	M	N	Y
2. MPF excitable	(Y)	(Y)	(Y)	(Y)	(M)	Y	Y	(N)
3. MPF bistable	(Y)	(Y)	(Y)	(Y)	(Y)	Y	Y	(N)

Observation 3 is not included because [Ca²⁺]_i spikes or sinusoidal oscillations are imposed in all of the simulations. Y, simulation predicts or does not dispute observation; N, simulation disputes observation; M, simulation allows, but does not require observation; —, simulation does not consider observation. The entries in parentheses indicate that at elevated [Ca²⁺]_i (as in Xenopus) these systems are oscillatory and the MPF frequency is modulated by the sinusoidal [Ca²⁺]_i signal (see text for details).